The present invention relates to an air suspension apparatus which is advantageously used for, for example, a suspension apparatus for a vehicle.
Generally, an air suspension apparatus mainly comprises a hydraulic shock absorber for generating a damping force for damping vibration, following extension and compression strokes of a piston rod and an air spring provided on an outer circumferential side of the hydraulic shock absorber so as to define an air chamber in which compressed air is sealably contained. The air spring biases the piston rod of the hydraulic shock absorber in a direction of extension.
Further, a suspension apparatus capable of controlling a damping force in accordance with variations in vehicle weight has been known [reference is made to, for example, Unexamined Japanese Patent Application Public Disclosure (Kokai) No. 57-205208].
The air suspension apparatus of Kokai No. 57-205208 mainly comprises: a cylinder; a piston slidably provided in the cylinder so as to divide an interior of the cylinder into two oil chambers; a piston rod having a proximal end portion thereof fixed to the piston and a distal end portion thereof protruding to the outside of the cylinder, the piston rod including an axial rod insertion hole; a hydraulic fluid passage formed in the piston rod so as to enable communication between the two oil chambers in the cylinder; a shutter slidably provided at a position in the hydraulic fluid passage for varying a flow path area of the hydraulic fluid passage to adjust a damping force; an actuator provided at the protruding end portion of the piston rod so as to operate the shutter; a transmission rod axially extending in the rod insertion hole in the piston rod so as to transmit an operating force of the actuator to the shutter; and an air spring provided between the cylinder and the protruding end portion of the piston rod so as to bias the piston rod in a direction of extension, the air spring including an air chamber in which compressed air is sealably contained.
The actuator includes a movable inner wall provided therein so as to define a pressure-receiving chamber for receiving air pressure. Movement of the movable inner wall is transmitted to the transmission rod through a cam member or the like. Further, an external pipe is provided between the pressure-receiving chamber in the actuator and the air chamber in the air spring so that the pressure of air in the air chamber is introduced into the pressure-receiving chamber through the external pipe.
The pressure in the air chamber varies, depending on the load (luggage or the like) carried by a vehicle. This pressure existing in the air chamber is introduced through the external pipe into the pressure-receiving chamber in the actuator, thus displacing the movable inner wall according to a change in pressure in the pressure-receiving chamber. Movement of the movable inner wall is transmitted from the transmission rod through the cam member or the like to the shutter. Consequently, the shutter slidably moves, to thereby change the flow path area of the hydraulic fluid passage, so that a damping force is varied automatically in accordance with the weight of the vehicle.
However, in the above-mentioned air suspension apparatus, the air chamber in the air spring and the pressure-receiving chamber in the actuator communicate with each other through the external pipe. Thus, there is a possibility of the occurrence of air leakage due to connection failure or breakage of the external pipe. This leads to a lowering of durability and reliability of the air suspension apparatus.
Further, when the external pipe is used, it is necessary to provide connecting holes for use in connecting the external pipe to the air spring and the actuator. Therefore, the number of necessary parts becomes large and a cumbersome operation for piping is necessary, leading to low productivity and high cost.